This invention relates to ignition systems of internal combustion engines, and more particularly, it is concerned with an ignition system of an internal combustion engine suitable for use with a chain saw, a mowing apparatus, an engine-driven sprayer, etc., of a portable type.
In one ignition system of the prior art suitable for use with the aforesaid type of engine, a permanent magnet having a positive pole and a negative pole is mounted to a rotary member, such as a flywheel, of the associated internal combustion engine and acts on a generating coil while the flywheel rotates to cause same to generate an electromotive force to produce an electric current which flows from the generating coil to an ignition capacitor to charge same. Then, the magnet causes the generating coil to generate a counter electromotive force to cause a thyristor of an ignition circuit to turn on, thereby causing the ignition capacitor to begin to discharge to produce a high voltage in an ignition coil, thereby causing a spark discharge to take place in an ignition plug of the internal combustion engine.
The ignition system of the aforesaid construction of the prior art is unable to cause a spark discharge to occur in the ignition plug at a timing optimum for the range of low engine speeds and the range of high engine speeds. The chain saw, mowing apparatus and engine-driven sprayer of the portable type generally operate in a condition in which the throttle is fully open or fully closed, and it is rare that they operate in a condition in which the throttle remains partly open. Thus, the problem raised with this type of ignition system is that it reduces the efficiency of the internal combustion engine.